Artificial hair that is used as filaments for wigs is required to have flame retardancy and heat resistance in addition to a clear color, natural gloss, lightweight, heat resistance, a soft touch feeling, flexibility, and the abilities to form and retain curls. As used herein, the term “flame retardancy” is defined as a self extinguishing property and the anti-dripping property of molten polymers. The term “heat resistance” refers to the property of hair to resist the temperature at which curls can be formed by a hair iron, without being shrunk or deformed by thermal stress. Heat resistance and flame retardancy are the most important properties required for artificial hair filaments that perform the function of human hair.
PVC filaments or modacrylic filaments have been used as filaments for wigs. These filaments have very excellent flame retardancy, but have the disadvantage of insufficient heat resistance because of their low softening temperature, and for this reason, the use thereof in applications requiring heat resistance is limited.
To overcome this disadvantage, polyester artificial hair based on a resin having a relatively high heat distortion temperature is used. Examples of the resin that is used for polyester artificial hair include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene terephthalate (PPT), polycyclohexanedimethanol terephthalate (PCT), polynaphthalene terephthalate (PEN), etc. These polyester resins have a relatively high heat resistance, but are flammable resins that are easily burned and have the property of dripping high-temperature molten polymer drops upon contact with flames. Thus, in order to use these resins as artificial hair, flame retardancy needs to be imparted to these resins. Artificial hair has a thickness of 40-100 denier (corresponding to 40-100 μm), which is thicker than that of filaments for clothes. Because artificial hair is connected to the scalp or hair of a person who wears a wig, a high degree of flame retardancy needs to be imparted to the artificial hair in order to protect the wig-wearing person from a burn upon contact with flames.
A number of technologies for imparting flame retardancy to flammable thermoplastic polyester resins to use the resins as artificial hair are known.
Polyester resins are flammable, easily catch fire and are rapidly burned while dripping high-temperature molten polymer drops.
An attempt was made to use a copolymer resin synthesized by adding phosphorus (P) atoms during a polyester preparation process, but it was difficult for phosphorus atoms to provide sufficient flame retardancy to the resin for use as artificial hair. For this reason, a number of artificial hairs containing a polymeric brominated flame retardant are known.
U.S. Pat. Nos. 7,759,429, 7,759,430, 8,211,542 and 8,211,542 disclose a flame retardant polyester artificial hair containing a brominated epoxy flame retardant. However, the brominated flame retardant used in these patents has a shortcoming in that it has artificial hair becomes heavy due to the high specific gravity of the flame retardant, and thus has poor wear feeling. In addition, there is a problem in that bromine gas harmful to workers is generated in a process of compounding the polyester resin with the brominated flame retardant and a high-temperature melt spinning process. Further, workers can also be exposed to bromine gas in a process of drawing or heat-treating undrawn yarns. In a wig making process, workers are exposed to the same harmful gas when forming curls at a temperature of 100˜130° C. for a long period of time. The biggest problem is that when the wig product is disposed of by incineration, large amounts of bromine compounds are discharged in a gaseous state to cause atmospheric pollution. For this reason, there is also a problem in that polymer fragments that are generated in a process of making frame-retardant polyester artificial hair are disposed of as waste without being recycled. Moreover, a wig made of polyester artificial hair containing the brominated flame retardant can be harmful to a person who wears it, because it is used in close contact with the scalp of the person. Thus, there is a need for new flame-retardant polyester artificial hair containing no brominated flame retardant. US Patent Publication No. 2012/0122843A discloses a thermoplastic polyester filaments containing a polymeric phosphorus-based flame retardant. The polyester filaments disclosed in this US Patent Publication comprises, in addition to a polyester resin, a polymeric phosphorus-based flame retardant that is a phosphonate-containing polymer, copolymer or oligomer. The polymeric phosphorus-based flame retardant has a weight-average molecular weight ranging from 10,000 to 120,000. However, the technology disclosed in this patent publication has the following problems that make it very difficult to produce an artificial hair filaments having a thickness of about 40-80 denier.
Conventional processes for producing flame-retardant polyester artificial filaments include a process of compounding raw materials, a melt spinning process, a drawing process and a heat treatment process. In the melt spinning process, a plurality of molten filaments are discharged through a plate nozzle below a die mounted at the front end of an extruder to form a filaments. The barrel temperature of the extruder is 250˜280° C., and the temperature of the die and the nozzle portion is 280˜290° C. However, if the polyester filaments containing the polymeric phosphorus-based flame retardant is used in a system for making polyester artificial hair containing a conventional brominated flame retardant, the following problems will arise.
The glass transition temperature (Tg) of the polymeric phosphorus-based flame retardant used is lower than that of the conventional brominated flame retardant by 40˜50° C., and the flow rate of the molten polymer at the temperature of the die and the nozzle is very high. Further, if the polymeric phosphorus-based flame retardant is added in an amount of 10-30 parts by weight based on 100 parts by weight of the polyester resin, the polyester resin will contain a large amount of phosphorus (P) which reduces the melt viscosity of the polyester resin.
As a result, when phosphorus-based artificial hair having a thickness of 40-80 denier is to be produced, the discharge of the polymer from the lower portion of the nozzle in the melt spinning process will not be uniform, and the melt tension of the molten polymer will be reduced, making it impossible to wind undrawn yarns having a specific thickness. Further, filament breakage will occur during melt spinning, making it impossible to continuously prepare undrawn yarns, and a filaments obtained by drawing and heat-treating prepared drawn yarns will have low strength and elongation, and thus cannot be used as artificial hair.
The present inventor has developed a phosphorus-based flame retardant polyester filaments for artificial hair, which does not cause the above-described problems even when it contains the polymeric phosphorus-based flame retardant, and a method for preparing the filaments.